Osteoporosis is a systemic disease that develops due to reduction of the bone volume or the bone mineral content and causes the breakage of the fine structure of bone, which reduces the bone strength and increases the risk of bone fracture. The number of patients with osteoporosis in Japan reaches about 11 million, and 80% of them are women. Osteoporosis mainly affects people in their middle or older age, and considering that the society is aging, the number of patients is expected to increase in the future. Another concern is that the incidence of bone fracture is increasing in elementary and junior high school students. In order to prevent osteoporosis, it is very important to substantially increase the bone mineral content during the young age, thus achieving a high peak bone mass. Thus the maintenance of bone health is now a social interest regardless of sex and age.
Bone diseases are conventionally prevented or treated by dietary calcium supplementation, light exercise, sun bath, medication, etc. Such dietary calcium supplementation is done with calcium salts such as calcium carbonate and calcium phosphate, and natural calcium sources such as bovine bone powder, egg shells and fish bone powder. However, such ingredients are not very suitable for oral ingestion in terms of solubility, absorptivity and taste. Moderate exercise increases the bone volume and strengthens bone, and a stroll and a walk are good for bone health. However, for people with low physical strength, even light exercise is troublesome, and exercise is almost impossible for the bedridden elderly. Sun bath is considered to be good for supply of activated vitamin D3, but sun bath is insufficient for prevention or treatment of bone diseases.
For the prevention or treatment of various chondropathies, the growth of chondrocytes and the expression of differentiation function are important. That is, the growth and maturation of chondrocytes are considered to promote normal growth of bone and repair bone fracture. Several factors for inducing the growth of chondrocytes have been reported, including transforming growth factor (TGF)-β1, insulin-like growth factor (IGF)-1, basic fibroblast growth factor (bFGF), PTH-related peptide (PTHrP), hepatocyte growth factor (HGF), and bone morphogenetic protein (BMP). However, clinical applications of chondrocyte growth-promoting drugs excellent in safety, stability and efficacy have not been established yet.
Patients with osteoarthritis account for the largest proportion of chondropathy patients. One of the causes of osteoarthritis may be aging, and the incidence of the disease is expected to increase in this aging society. Conventionally, bone resorption inhibitors such as estrogen and calcitonin, aspirin, and nonsteroidal anti-inflammatory drugs (NSAIDs) have mostly been used for the prevention and treatment of cartilage disorders that manifest degeneration of cartilage as major symptoms, such as joint diseases. However, these drugs are not effective enough, and are well-known to cause adverse reactions such as digestive tract disorders. Under these circumstances, there has been a great demand for prophylactic or alleviating drugs that are safe for use in the treatment of cartilage injuries and cartilage disorders.
The inventors found that an egg yolk-derived peptide comprising an amino acid sequence comprising at least Ala-Glu-Ser has osteoblast growth-promoting activity (see Patent Literature 1) and that an egg-yolk protein hydrolysate has chondrocyte growth-promoting activity (see Patent Literature 2). The inventors then filed a patent based on these findings.